I am giving a lecture in IT (for the first time) to more than 100 students. I refused to use the slides of the previous lecturer and I wanted to make my owns. They take me a lot of effort and I believe that are better than most lecture slides on the same topic.

The lecture includes so many mathematical equations (almost every slide). Because I am making them from scratch, I made already 3 mistakes in the equation (e.g. multiplication instead of addition). I discovered two of them during the lecture I said that it is a mistake. I corrected the mistakes before I uploaded the slides.

the third mistake I did not notice but when I gave an example I used the correct one. In the exercise, the students were claiming that the equation does not give the same result as expected in the exercise (which is graded). I decided to give all the students the full note for that exercise.

My question is how bad to have these mistakes? Should I use the slides of the previous lecturer?

  • Your question is meant in the sense of evaluations? Then you would need to state your university's policy on that. In my university, letting students do evaluations is (almost) optional -- while your superiors could look into your evaluations, in reality nobody (than yourself) cares about them.
    – user115896
    Commented Nov 28, 2019 at 16:02
  • for me also is optional. I am talking from a perspective that whether this makes a bad lecturer. A bad evaluation for my first lecture will just hurt because of the effort I am putting.
    – Yacine
    Commented Nov 28, 2019 at 16:05
  • "Should I use the slides of the previous lecturer?" How confident are you that the previous lecturer's slides have fewer errors than your own slides? Commented Nov 28, 2019 at 17:04
  • @Andreas Blass That is actually a good point!
    – Yacine
    Commented Nov 28, 2019 at 17:19
  • 1
    Making mistakes can be good. I tell my students upfront, there are errors on my slides. Be vigilant! So I sometimes 'stumble' along, and keep them on their toes. As long you know what you are talking about, it is all good. Commented Nov 29, 2019 at 7:57

4 Answers 4


Everyone makes mistakes. Teachers, students, everyone. It isn't terrible that you make them, but it is good, and can be extremely instructive when you correct them.

Your description suggests that you do the right thing here. Proof your slides and make corrections. But also, when mistakes are pointed out in class, not only admit them readily, but work through the correction as needed. If it is just a typing error then it is easy, but logic errors might require more effort.

However, seeing a professor work in real time to solve a problem, rather than just showing prepared stuff is extremely enlightening. Students can get the idea when presentations are perfect that this stuff is supposed to be easy. In fact, it may not be easy and so seeing a solution develop, even seeing false starts and corrections, will give them more confidence in their own work. Especially if they struggle with some of the ideas.

Your students will be evaluating you overall, not just your slides. If you act in a human and humane manner, especially by responding to their needs, you should do fine. But occasionally a student will be unreasonable. Don't worry too much about this.

But perfection in a lecture isn't necessarily the most effect way to teach. That doesn't excuse sloppiness, of course, but consider the overall picture, not just the minute details.

I've had students complement me more often on "lectures" that forced me to work "live" than on those that were very polished. In fact, I once tried to develop a "perfect" description of a hard problem and it left the student baffled. "Where did that come from?"

Be good. Very good. But recognize that you are human, which means being adaptable.

As to using the previous slides, I have no opinion. They might be good, but they might be too perfect. They might also force you into stilted delivery, which you should avoid.

But as a newcomer to this stuff, you might have conversations with colleagues about your teaching materials and get their feedback. People learn a lot by interacting with students, but it isn't obvious to a new teacher how that all fits together effectively. Some places have more senior instructors visit the classes of new faculty and then give feedback, either formally or informally. There is no real reason why you can't ask a trusted colleague to do that, even if not required. While it might feel risky, it also shows you are trying to improve your craft.

  • Can you explain what you mean by "perfect description"? Do you mean something like a logical correct proof without any indication where the ideas come from? Because then I don't understand what this has to do with mistakes on slides?
    – user115896
    Commented Nov 28, 2019 at 18:41
  • It can mean a lot of things, but "slick" isn't necessarily good. But, no, proofs should be correct. Insights shouldn't be ignored, of course. The key idea, perhaps, is that students need to be engaged in learning so something that is too perfect may let them think they understand something that they really do not.
    – Buffy
    Commented Nov 28, 2019 at 18:58
  • I agree with you -- good pedagogy presents insights -- but what does this have to do with the kind of mistakes the OP describes?
    – user115896
    Commented Nov 28, 2019 at 20:01
  • @Heutl, you can capitalize on mistakes when you make them to direct the students into deeper understanding. Make it an opportunity. Not every such mistake is fruit here, but look for the chances.
    – Buffy
    Commented Nov 28, 2019 at 20:21
  • 1
    @Heutl, I agree. My answer is more general than the question. That is actually a positive value here. Future visitors may have similar, but not identical, situations. If we do no more than answer the question and only for the OP then this site is no better than a chat room.
    – Buffy
    Commented Nov 28, 2019 at 21:29

If you are averaging 3 errors/lecture*, that's too much, especially with typed materials. Makes the course hard to follow and creates a real confusion factor of people using the uncorrected materials in error.

Not sure if the solution is to use the previous materials or just tighten up on what you are doing yourself. I suspect there is some way to be better prepared without just using old slides (which may have issues themselves). Wonder if you are somehow trying to be too ambitious. All that said, if you are not so strong on the materials yourself, perhaps using old lecture materials, at least for first run through a class, might be a better course of action. After doing that, you are more knowledgeable about what you want to change and why.

P.s. I hate slides--find blackboard and chalk much more engaging. (But that's off topic.)

*If instead, this was 3 mistakes over an entire course's typed notes, than no biggie.

  • 3 errors/ 9 lectures till now, bit still 6 are remaining
    – Yacine
    Commented Nov 29, 2019 at 6:14
  • That's OK. There might be other reasons to evaluate if you should do your own stuff or use pre-existing. But not the corrections.
    – guest
    Commented Nov 29, 2019 at 16:02
  • Personally, I like to first have a mixture of my own and previous lecture slides to begin with and then slowly create my own for sections as I see fit. We don't have to reinvent the wheel every time.
    – NoName
    Commented May 27, 2021 at 23:27

Well, first up be frank with the students and then give them some freeby decimals on their grade as apology because if they study from the mistakes they will get it wrong in the exams (besides the full note you already gave), and to avoid it, start a mistake hunt.

Give your students ALL the slides and tell them to analyze them and submit the mistakes they find or improvements they can think off, you can do this as part of the grading as some homework project or you can add it as an optional with an extra point or 2 over the final grade, that will be a nice incentive. In the end you can find even more mistakes you didn't noticed, improve the layout or design, have the students study and work, and all resulting into material you can use later on in the future. And your evaluation will be saved.


Making a good slide deck is really, really hard. It is entirely normal that a lecturer needs several years teaching a course to develop the perfect deck.

Consider the purpose of the slides: to give the students the best possible education. If your current deck isn't good enough yet, you should really consider using some of the old deck. There's nothing wrong with using a blend, as long as you give credit to your predecessor. If you really don't like the old deck, you can also look for slide decks for the same topic produced at other universities.

Making good slides is so hard actually, that it's quite normal for a really good slide deck to get used by many grateful lecturers at multiple institutions. For the original creator, this can lead to a lot of name recognition, as someone making a valuable contribution to the community. (Remember to put your name and institution in the footer of your slides.)

Finally, be honest with your students. Encourage them to ask questions, if they think there may be a mistake in a slide. Either in class of privately. Either you find and fix a mistake in your slide (and discover a smart student), or you get to explain to your student why your slide is correct after all (and the student learns something).

  • I regularly make scrapbooks with Google Slides. This is my rough book "Scrapbook Tutorials." In other words, it is incomplete. Just go to page 2. Links are embedded inside slanted text boxes. docs.google.com/presentation/d/…
    – user92331
    Commented Dec 1, 2019 at 18:39

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